Roundcube

Roundcube is a browser-based IMAP webmail client that runs entirely in the browser but feels like a native desktop email app. It's built for anyone who wants to self-host their email interface without sacrificing the features they'd expect from a full client. Organizations, hosting providers, and individuals running their own mail servers are its natural fit.

The interface handles the day-to-day email workflow well. Drag-and-drop message management, threaded message listing, and find-as-you-type address book lookup keep common tasks fast. HTML and MIME messages are fully supported, and spell checking is built in.

Key capabilities include:

• Address book with group support, LDAP connectors, and seamless compose integration
• Multiple sender identities for managing different email personas from one account
• PGP encryption support for end-to-end secure messaging
• Shared and global IMAP folders with access control lists (ACL)
• IDNA and SMTPUTF8 support for internationalized email addresses
• Built-in caching for faster mailbox access on large accounts
• Responsive skin that adapts across desktop, tablet, and mobile
• Plugin API for extending functionality without modifying core code
• Import/export for contacts and data portability
• XSS protection baked into the interface

There's no cap on users or messages, which makes it practical for shared hosting environments or small organizations running their own infrastructure. The plugin system means the core stays lean while allowing integrations and customizations to be layered on top.

If you're looking at other self-hosted email tools, Twake Mail and Billion Mail take different approaches worth comparing. For teams that need email marketing alongside inbox management, something like Sendportal covers that separate use case.